The present invention relates to a process for the liquid phase acylation of aromatic compounds by an acylating agent using a solid catalyst comprising metal oxide(s). The present invention particularly relates to a process for the acylation of aromatic compounds using a reusable solid catalyst comprising metal oxide(s).
Friedel Crafts type acylation of aromatic compounds by various acylating agents, using homogeneous Lewis acid catalysts, such as AlCl0, BF3, ZnCl2 and other metal chlorides and protonic acid catalysts such as H2SO4, H3PO4, HF, etc., are well known in the art [G. A. Olah, in Friedel Crafts and related reactions: vol III, Acylation and related reactions, Wiley-Interscience Publ., New York, 1964].
U.S. Pat. No. 5,476,970 granted to Rains et al. Discloses a homogeneous liquid phase process for the acylation of R1R2R6H4 by R3R4R6H3COCl, wherein R1, R2, R3 and R4 are chemical groups using FeCl3 catalyst at high pressures. French Patents FR 2768728 (1999) and FR 2768729 (1999) of Baudry et al, disclose liquid phase homogeneous process for the benzoylation of anisole by benzoyl chloride using rare earth halides or uranyl halide.
Japanese patent JP 08277241, A2 (1996) of Kunikata discloses a liquid phase process for the acylation of phenol by phenyl acetyl chloride using a homogeneous AlCl0 catalyst. A use of AlCl0 as a homogeneous catalyst is also disclosed by Oono for the acylation of toluene with acetyl chloride at high pressures in Japanese patent JP 09059205, A2 (1997). Japanese patent JP 20000086570, A2 (2000) of Shoji et al discloses a homogeneous liquid phase process for the acylation of toluene by acetyl fluoride using HF-BF3 as a catalyst.
The main disadvantages of the Friedel-Crafts type acylation processes based on the use of the above mentioned homogeneous acid catalysts are:
1. The separation and recovery of the dissolved acid catalysts from the liquid reaction mixture is difficult.
2. The disposal of the used acid catalysts creates environmental pollution.
3. The homogeneous acid catalysts also result in problems such as high toxicity, corrosion, spent acid disposal and also require use of more than the stoichiometric amounts.
Liquid phase processes for the acylation of aromatic compounds by acyl halides using solid catalysts is also well known in the art.
Japanese patent JP 01089894, A2 (1995) to Myata et al discloses a liquid phase process for the acylation of toluene with benzoyl chloride using ammonium chloride treated H-beta zeolite catalyst under reflux for 3 hours to get para acylated toluene with 28% yield. French patent FR 2745287, A1 (1997) of Barbier et al discloses a liquid phase acylation of anisole by benzoyl chloride under reflux using neodymium chloride deposited on montmorillonite Kxe2x80x9410 clay.
Vincent et al (ref Tetrahedron Lett., 35, 1994, 2601) disclose that H-ZSM-5 zeolite can catalyze the acylation of phenol and anisole by benzoyl chloride at 120xc2x0 C. for 5 hours but not the acylation with benzoyl chloride of benzene and naphthalene.
Acylation of aromatic compounds involves the electrophilic substitution of H from the aromatic nucleus of the aromatic compound. It is well known in the prior art that the electrophilic substitution is favoured by the presence of electron donating groups such as OH, alkyl, alkoxy, phenoxy, amine, alkyl amine, SH, etc., in the aromatic compound. Whereas the electophilic substitution is inhibited by the presence of electron withdrawing groups such as halo, nitro, cyano. Carboxy, aldehyde, etc., in the aromatic compound [G. A. Olah, in Friedel Crafts and related reactions Wiley-Interscience Publ., New York, 1963].
While some limitations of the homogeneous acid catalysed processes are overcome in the prior art heterogeneous solid catalysed processes described above, the acylating activity of the solid acid catalysts used in the prior art processes is low, particularly for acylating aromatic compounds not containing electron donating groups, such as benzene, naphthalene etc. Both the prior art homogeneous and heterogeneous acid catalysts are highly moisture sensitive, and hence demand moisture free or thoroughly dried reactants, solvents and catalyst for Friedel-Crafts type acylation processes. In the presence of moisture in the reaction mixture, both the above homogeneous and heterogeneous catalysts show poor activity in the Friedel-Crafts type acylation processes. Hence there is a need for finding more efficient, reusable and also moisture insensitive solid catalyst for the acylation of aromatic compounds, which overcomes the disadvantages of the prior art discussed above.
The main object of the present invention is to provide a liquid phase process for the acylation of aromatic compounds including those which do not contain electron donating groups, using a solid catalyst, which has high activity when the aromatic ring activating groups (electron donating groups like alkyl, alkoxy, hydroxy, phenoxy, etc.) are present in the aromatic ring to be acylated and also when the ring activating groups in the aromatic ring to be acylated are absent, such that reaction temperature is low and/or reaction time is short.
Another object of the invention is to provide a liquid phase process for acylation of aromatic compounds using a solid catalyst that is easily separable and reusable in the process.
It is another object of the present invention to provide a liquid phase process for the acylation of aromatic compounds that is insensitive the presence of moisture in the reaction mixture.
Accordingly the present invention provides a liquid phase process for the acylation of aromatic compound of the formula (R1R2R3R4)xe2x80x94Mxe2x80x94H by an acylating agent of the formula (R5R6R7)xe2x80x94Yxe2x80x94Z to obtain the corresponding acylated compound of the formula (R1R2R3R4)xe2x80x94Mxe2x80x94Yxe2x80x94(R5R6R7), wherein M is an aromatic nucleus with R1R2R3, and R4 being the chemical groups attached thereto, Y is the nucleus of the acylating agent and is selected from the group consisting of Cxe2x80x94CO, CnH2nxe2x88x922CO, C6H2CO, C6H2CnH2nxe2x80x94CO and C6H2Cnxe2x88x921(X)xe2x80x94CO with R5, R6 and R7 being chemical groups attached thereto Y, Z is selected from the group consisting of Cl, Br, I and OH, X is a halogen, and n is an integer having a value equal to or greater than 1.0, using a solid catalyst comprising a metal oxide of the formula AOx with or without a catalyst support, wherein A is a metallic element selected from Ga, In, Tl, Fe and a mixture of two or more thereof, and x is the number of oxygen atoms required to fulfil the valance requirement of A, the said process comprising,
i. pretreating the solid catalyst by contacting it with a dry gas comprising a hydrogen halide in the presence or absence of the aromatic compound to be acylated;
ii. contacting the hydrogen halide pretreated catalyst with a liquid reaction mixture comprising the aromatic compound and the acylating agent in a stirred batch reactor at following reaction conditions: weight ratio of catalyst to acylating agent in the range of about 0.01 to about 2.0, mole ratio of the aromatic compound to the acylating agent in the range of from about 0.1 to 100, weight ratio of non-aqueous solvent to the aromatic compound being in the range of about 0 to about 100, reaction temperature being in the range of about 10xc2x0 C. to about 300xc2x0 C., pressure in the range of about 0.5 atm to about 10 atm., gas hourly space velocity of inert gas bubbled through the reaction mixture being in the range of about Ohxe2x88x921 to 5000 hxe2x88x921 and reaction period in the range of from about 0.02 hours to about 100 hours;
iii. cooling the reaction mixture to a temperature of about 30xc2x0 C., removing the catalyst from the reaction mixture by filtration and then separating the reaction products from the reaction mixture.
In another embodiment of the invention, R1R2R3, and R4 are each selected from hydrogen, alkane, olefininc, phenyl, alkoxy, phenoxy, hydroxyl, aldehydic, halogen, ketonic, amine, amide, thio, and sulphonic acid groups; Z is selected from Cl, Br, or OH, each of R5R6, and R7 is selected from the group consisting of hydrogen, alkane, olefinic, phenyl, halogen, nitro and cyano groups, A is selected from Ga, In and Tl or a mixture of two or more thereof, the hydrogen halide used in step ii is selected from HCl and HBr, the weight ratio of the catalyst to the acylating agent is in the range of about 0.03 to 0.09, the mole ratio of the aromatic compound to the acylating agent is in the range of 1.0 to 20, the weight ratio of the non-aqueous solvent to the aromatic compound is in the range of 0 to 20, the reaction temperature is in the range of 20xc2x0 C. to 200xc2x0 C., the reaction pressure is in the range of 1 atm to 5 atm, the reaction period is in the range of 0.05 hours to 20 hours, and the space velocity of inert gas is in the range of 50hxe2x88x921 to 500hxe2x88x921.
In another embodiment of the invention, M is selected from the group comprising a single aromatic ring containing 6 C atoms and 1 H atom, fused two aromatic rings containing 10 C atoms and 3 H atoms, and three fused aromatic rings containing 14 C atoms and 5 H atoms.
In one embodiment of the invention, the used catalyst is washed with a non-aqueous solvent or aromatic substrate; and recycled directly with or without drying, to step i above.
In another embodiment of the invention, R1R2R3, and R4 are each selected from the group consisting of H, CnH2n+1, CmH2m+1, C6H5, CnH2nC6H5, OH, OCnH2n+1, O C6H5, halogen, NO2, NH2, NH CnH2n+1, N(CnH2n+1)2,NHCO CnH2n+1, NHCOC6H5, CN, CHO, COOH, COOCnH2n+1, COCnH2n+1, SO3H, SO3CnH2n+1, SH, alkyl mercapto and aryl mercapto wherein n and m are integers greater than or equal to 1 and 2 respectively.
In another embodiment of the invention, each of R5, R6, and R7 is selected from the group consisting of H, CH3, C2H5, OH, OCH3, OC2H5, NO2, halogen and NH2.
In another embodiment of the invention, the preferred reaction temperature is in the range of 20xc2x0 C. to 200xc2x0 C., the preferred reaction time period is in the range of 0.1 hours to 20 hours, the preferred gas hourly space velocity of the inert gas bubbling through the reaction mixture is in the range of 50hxe2x88x921 to 500hxe2x88x921, the weight ratio of the catalyst to the acylating agent is in the range of about 0.1 to 1, the mole ratio of the aromatic compound to the acylating agent is in the range of 0.5 to 20, the weight ratio of the non-aqueous solvent to the aromatic compound is in the range of 0 to 20, Z is preferably Cl or Br, M is Ga or In or a mixture thereof, the preferred hydrogen halide used in step i is HCl or HBr, R1, R2, R3, and R4 are each selected from the group consisting of H, alkane (CnH2n+1), olefinic (CmH2m+1), phenyl (C6H5), alkoxy (OCnH2n+1), phenoxy (OC6H5), hydroxyl (OH), aldehydic (CHO), ketonic, amine (NH2), amide (CO NH2), sulfonic acid (SO3H), and thio (SH), wherein n and m are integers greater than or equal to 1 and 2 respectively, each of R5, R6, and R7 is selected from the group consisting of H, alkane(CnHn+1), olefinic (CmH2m+1), phenyl (C6H5), haloge (Cl, Br, I or F), nitro (NO2), and cyano (CN).
In another embodiment of the invention, the catalyst is supported on a meso or macroporous catalyst carrier selected from alumina, silica, silica-alumina, inert metal oxides, zeolites, and zeolite like materials.
In a further embodiment of the invention, the catalyst support comprises a zeolite material selected from the group consisting of microporous zeolites (pore sizexe2x89xa61.0 nm) such as zeolite X, zeolite Y, mordenite, Zeolite L, zeolite beta, ZSM 5, ZSM 8, ZSM 11, and mesoporous zeolites (pore size=1.5 nm to 50 nm) such as M41S type material, MCM 41.
In another embodiment of the invention, the solvent when used is selected from the group consisting of dichloroethane, nitrobenzene, nitromethane, chlorobenzene, n-hexane, n-heptane and n-octane.
It is observed that the catalyst used in the invention has a high activity in the acylation of aromatic compounds not only when electron donating groups, which is the aromatic ring activating group, is present in the aromatic ring to be acylated, but also when it is absent. Without being bound by the proposition, it is believed that this leads to lowering of the reaction temperature and reaction time requirements.
Another advantage observed is that the solid catalyst used can be separated and reused repeatedly in the process. It is also observed that the reaction rates are high even in the presence of moisture in the reaction mixture. Pretreatment of the solid catalyst with a hydrogen halide is essential in order to activate the catalyst.
The catalyst is supported on a meso or macroporous catalyst carrier selected from alumina, silica, silica-alumina, inert metal oxides, zeolites, and zeolite like materials. The zeolite material is selected from the group consisting of microporous zeolites (pore sizexe2x89xa61.0 nm) such as zeolite X, zeolite Y, mordenite, Zeolite L, zeolite beta, ZSM 5, ZSM 8, ZSM 11, and mesoporous zeolites (pore size=1.5 nm to 50 nm) such as M41S type material, MCM 41. (Breck, Zeolite Molecular Sieves, Wiley Interscience Publ., New York, 1974; Beck et al, J. Am. Chem. Soc., vol. 114, page 10834, 1992; Nature (London) vol. 359, 710, 1992).
In general, micropores have diameter below 1 nm, mesopores have diameter between 1 nm and 20 nm and macropores have diameter above 20 nm. The catalyst supported on a microporous catalyst carrier is used generally when the both reactants have minimum molecular diameter or critical size of less than 0.7 nm. The mesoporous or macroporous catalyst carriers can be used irrespective of the size of the reactants. The reaction is carried out in a stirred batch reactor fitted with a reflex condenser and an arrangement for bubbling inert gas through the reaction mixture. Such arrangements are known in the art for liquid phase reactions.
In the reaction, the main product formed is the acylated aromatic compound of the formula (R1R2R3R4)xe2x80x94Mxe2x80x94Yxe2x80x94(R5R6R7) while HZ is formed as a byproduct wherein R1, R2, R3, R4, M, Y, R5, R6, and R7 and Z are as described above.
The process of the invention can be carried out with or without a non-aqueous solvent selected from dichloroethane, nitrobenzene, nitromethane, chlorobenzene, n-hexane, n-heptane and n-octane. The role of the solvent is to dissolve the solid reactant or reactants and thereby facilitate the reaction there between. The solvent is not necessary when both the reactants are liquid at reaction conditions. It is observed that the solvent when used is not converted during the process.
The inert gas is bubbled continuously through the reaction mixture in order to remove the byproduct form reaction mixture and thereby prevent or minimise reverse reaction. This helps to shorten the time of the reaction. The reaction takes place even in the absence of the inert gas but requires a longer time period and leads to incomplete conversion.
The reflux condenser fitted with the reactor is to condense the reactants and/or the solvent and to return them to the reaction mixture and allow the inert gas that is continuously bubbling through the reaction mixture to escape along with the reaction byproduct. The reaction pressure is normally above atmospheric pressure thereby allowing the reaction to proceed at a temperature higher than the normal boiling point of the reactants and/or solvent with increase in reaction pressure.
The catalyst used is heterogeneous with respect to the reaction mixture and can be removed from the reaction mixture by simple filtration and after washing with solvent or liquid aromatic compound which is to be acylated, recycled to the reaction mixture. The catalyst activates both the reactants and thereby increases the rate of the acylation reaction. During the pretreatment of the catalyst, the catalyst surface is changed by partial halidation causing modification of the active sites and/or creation of new active sites on the surface thereof. The pretreatment of the catalyst is critical to activate the catalyst. The pretreatment of the catalyst can be effected by:
1. contacting the solid catalyst with hydrogen halide gas in a closed vessel at room temperature for an effective period to activate the catalyst;
2. by passing a mixture of hydrogen halide and nitrogen or any other inert gas over the solid catalyst in a glass reactor at or above room temperature for a period of above 0.05 hours;
3. by passing a hydrogen halide gas with or without an inert gas such as nitrogen, argon, helium or the like through the reaction mixture containing the aromatic substrate, with or without the solvent, and the catalyst, in a stirred reactor at a temperature above about room temperature for a period above about 0.05 hours and then flashing the reaction mixture with an inert gas to remove physically adsorbed or absorbed hydrogen halide in the reaction mixture.